Green’s Dictionary of Slang

1. a cow-rustler, a person who steals or rebrands cattle.

1897		E. Hough Story of the Cowboy 279: A genuine rustler was called a ‘waddy,’ a name difficult to trace to its origins [DA].
1909		W.M. Raine Brand Blotters (1912) 36: I see. I’m a waddy and a thief, but you’re going to protect me for old time’s sake. That’s the play, is it?
1922		P.A. Rollins Cowboy 313: The movement had also militant apostles in the ‘waddies,’ men faithful to the illegal art of rustling.

2. a cowboy, esp. a temporary cowhand.

1908		‘Top Hand’ in Lingenfelter et al. Songs of the Amer. West (1968) 336: He rides a fancy horse, he is a favorite man, / Can get more credit than a common waddie can [...] From the top to the bottom, he’s a bold jackass, / Waddie cowboy.
1920–23		in J.M. Hunter Trail Drivers of Texas (1963) I 331: A cowboy is a ‘waddy’ or ‘screw’ or ‘buckaroo.’.
1938		B. Conlon ‘Rope Meat’ in Wild West Weekly 22 Oct. 🌐 The young waddy felt the two guns poked in his back.
1948		Kerouac letter 10 July in Charters I (1995) 159: The real work of castration of steers is the work of waddies, or vaqueros in Cal.
1954		Indep. Record (Helena, MT) 9 Oct. 3/7: Other westerners might be hay waddies (hay field workers) [...].